Novel silicone composition crosslinking catalysts

ABSTRACT

A crosslinked silicone material Y obtained by heating to a temperature of between 70 and 200° C., a crosslinkable composition X including an organopolysiloxane compound A containing, per molecule, at least two C 2 -C 6  alkenyl radicals bonded to silicon atoms; an organohydrogenopolysiloxane compound B containing, per molecule, at least two hydrogen atoms bonded to an identical or different silicon atom; a catalyst C of formula [Ni(L 1 ) 2 ] where Ni represents nickel at degree of oxidation II; L 1  which may be identical or different, represents a β-dicarbonylato anion or the enolate anion of a β-dicarbonylated compound; optionally an adhesion promoter D; and optionally a charge E.

FIELD OF THE INVENTION

This invention relates to the field of materials obtained by crosslinking of silicone compositions in which are put into contact reagents having at least two unsaturated bonds and organosilicon compounds having at least two hydrogenosilyated units (ESiH) in the presence of a catalyst C which is a complex corresponding to the following formula:

[Ni(L¹)₂]

in which the symbol Ni represents nickel at degree of oxidation II, and the symbols L′, which may be identical or different, represent a ligand which is a β-dicarbonylato anion or the enolate anion of a β-dicarbonylated compound.

TECHNOLOGICAL BACKGROUND

In the field of silicone composition crosslinking, hydrosilylation, also referred to as polyaddition, is a preponderant reaction.

During a hydrosilylation reaction, a compound comprising at least one unsaturation reacts with a compound comprising at least one hydrogen atom bonded to a silicon atom. This reaction can for example be described by the reaction equation (1) in the case of an unsaturation of the alkene type:

or by the reaction equation (2) in the case of an unsaturation of the alkyne type:

The hydrosilylation of unsaturated compounds is carried out by catalysis, using an organometallic catalyst. Currently, the suitable organometallic catalyst for this reaction is a platinum catalyst. As such, most industrial hydrosilylation reactions are catalysed by the Karstedt platinum complex, of general formula Pt₂(divinyltetramethyldisiloxane)₃ (or in abbreviated form Pt₂(DVTMS)₃):

At the beginning of the 2000's, the preparation of platinum-carbene complexes of general formula:

made it possible to have access to more stable catalysts (see for example international patent application WO 01/42258).

However, the use of organometallic platinum catalysts is still problematic. This is a toxic metal, expensive, and is becoming scarce and of which the cost fluctuates enormously. Its use on an industrial scale is therefore difficult. It is therefore sought to reduce as much as possible the quantity of catalyst required for the reaction, without however reducing the yield and the speed of the reaction. Moreover, it is sought to have a catalyst that is stable during the reaction. It has been observed that, during the catalysed reaction, the metal platinum could precipitate, which has the consequence of forming insoluble colloids in the reaction medium. The catalyst is then less active. In addition, these colloids form a cloud in the reaction medium, and the products obtained are not satisfactory from an aesthetic standpoint as they are coloured.

Finally, platinum based complexes catalyse the hydrosilylation reactions at ambient temperature with a rapid kinetics, of about a few minutes. In order to have the time to prepare, transport and implement the composition before it hardens, it is often necessary to temporarily inhibit the hydrosilylation reaction. For example, when it is sought to coat a paper or polymer substrate with a non-stick silicone coating, the silicone composition is formulated to form a bath that must remain liquid at ambient temperature for several hours before being deposited on the substrate. It is only after this depositing that it is desired for the hardening by hydrosilylation to occur. The introduction of hydrosilylation inhibiting additives makes it possible to effectively prevent the reaction as long as necessary before activation. However, it is sometimes necessary to use large quantities of inhibiting agent, which causes a strong inhibition of the hydrosilylation catalyst. This results in that the speed of hardening of the composition, even after activation, is slowed down, which is a major disadvantage from an industrial standpoint as this in particular requires reducing the coating speed and therefore the speed of production.

It would therefore be interesting to propose organometallic catalysts as an alternative to platinum based catalysts and to have new silicone materials that are crosslinked and/or hardened by means of catalysts that no longer have the problems described hereinabove, in particular that do not require the use of an inhibiting agent.

This objective is achieved using a catalyst which is a complex of nickel (II) that has a specific structure. These catalysts, in particular, do not require manipulation under protected atmosphere (for example under argon). The crosslinking reactions wherein they are implemented can also be carried out in air, without protected atmosphere.

This invention thus has for object, according to a first aspect, a crosslinked silicone material Y obtained by heating to a temperature of between 70 and 200° C., preferably between 80 and 150° C., and more preferably between 80 and 130° C., a crosslinkable composition X comprising:

-   -   at least one organopolysiloxane compound A comprising, per         molecule, at least two C₂-C₆ alkenyl radicals bonded to silicon         atoms,     -   at least one organohydrogenopolysiloxane compound B comprising,         per molecule, at least two hydrogen atoms bonded to an identical         or different silicon atom,     -   at least one catalyst C which is a complex corresponding to the         following formula:

[Ni(L¹)₂]

in which:

-   -   the symbol Ni represents nickel at degree of oxidation II,     -   the symbols L¹, which may be identical or different, represent a         ligand which is a β-dicarbonylato anion or the enolate anion of         a β-dicarbonylated compound,     -   optionally at least one adhesion promoter D and     -   optionally at least one charge E.

The term “crosslinked silicone material” means any silicone based product obtained by crosslinking and/or hardening compositions comprising organopolysiloxanes having at least two unsaturated bonds and organopolysiloxanes having at least two hydrogenosilylated units (≡SiH). The crosslinked silicone material can for example be an elastomer, a gel or a foam.

The invention also has for object, according to a second aspect, a crosslinkable composition X such as described hereinabove.

The composition X according to the invention is crosslinkable, i.e., in terms of this application, once the compounds A and B have reacted together in the presence of the catalyst C, a three-dimensional network is formed, which leads to the hardening of the composition. The crosslinking therefore implies a progressive physical change of the medium constituting the composition.

The publications Bogdan Marciniec et al. “Catalyst of hydrosililation Part XXV. Effect of nickel (o) and nickel (II) complex catalysts on dehydrogenative silylation, hydrosilylation and dimerization of vinyltriethaxysilane”, Journal of Organometallic chemistry, vol. 484, no. 1-2, 27 Dec. 1994 and “Catalyst of hydrosililation Part XX. Unusual reaction of vinyltriethaxysilane with triethaxysilane catalyzed by nickel acetylacetonate”, Journal of Organometallic chemistry, Lausane JOM, 15 Oct. 1991, describe a hydrosilylation reaction between two silanes, vinyltriethoxysilane (EtO)₃—Si-Vi and triethoxysilane (EtO)₃—SiH, in the presence of catalysts of nickel (0) or (2). Silanes comprising the Si—H bond have as substituents ethoxy Si—O-Et units that are very specific and very different from the siloxanes according to this application which have alkyl and siloxy substituents.

The invention also has for object, according to a third aspect, the use of the previously described catalyst C as silicone composition crosslinking catalyst.

The invention further has for purpose, according to a fourth aspect, a silicone composition crosslinking method, characterised in that it consists in heating the previously described composition X to a temperature of between 70 and 200° C., preferably between 80 and 150° C., and more preferably between 80 and 130° C., as well as the crosslinked silicone material Y obtained as such.

According to a particularly advantageous embodiment, the organopolysiloxane A comprising, per molecule, at least two C₂-C₆ alkenyl radicals bonded to silicon atoms, comprises:

(i) at least two siloxyl units (A.1), which may be identical or different, of the following formula:

$\begin{matrix} {W_{a}Z_{b}{SiO}_{\frac{4 - {({a + b})}}{2}}} & \left( {A{.1}} \right) \end{matrix}$

in which:

-   -   a=1 or 2, b=0, 1 or 2 and a+b=1, 2 or 3;     -   the symbols W, which may be identical or different, represent a         C₂-C₆ linear or branched alkenyl group,     -   and the symbols Z, which may be identical or different,         represent a monovalent hydrocarbon group having from 1 to 30         carbon atoms, and preferably chosen from the group consisting of         alkyl groups having from 1 to 8 carbon atoms and aryl groups         containing between 6 and 12 carbon atoms, and more preferably         chosen from the group consisting of a methyl, ethyl, propyl,         3,3,3-trifluoropropyl, xylyl, tolyl and phenyl radical,

(ii) and optionally at least one siloxyl unit of the following formula:

$\begin{matrix} {Z_{a}^{1}{SiO}_{\frac{4 - a}{2}}} & \left( {A{.2}} \right) \end{matrix}$

in which:

-   -   a=0, 1, 2 or 3,     -   the symbols Z¹, which may be identical or different, represent a         monovalent hydrocarbon group having from 1 to 30 carbon atoms         and preferably chosen from the group consisting of alkyl groups         having from 1 to 8 carbon atoms inclusive and aryl groups         containing between 6 and 12 carbon atoms, and more preferably         chosen from the group consisting of a methyl, ethyl, propyl,         3,3,3-trifluoropropyl, xylyl, tolyl and phenyl radical.

Advantageously, the radicals Z and Z¹ are chosen from the group consisting of a methyl and phenyl radical, and W is chosen from the following list: vinyl, propenyl, 3-butenyl, 5-hexenyl, 9-decenyl, 10-undecenyl, 5,9-decadienyl and 6-11-dodecadienyle, and preferably W is a vinyl.

These organopolysiloxanes can have a linear, branched, or cyclical structure. Their degree of polymerisation is, preferably, between 2 and 5000.

When it is a question of linear polymers, the latter are substantially constituted of siloxyl “D” units chosen from the group consisting of the siloxyl units W₂SiO_(2/2), WZSiO_(2/2) and Z¹ ₂SiO_(2/2), and siloxyl units “M” chosen from the group consisting of the siloxyl units W₃SiO_(1/2), WZ₂SiO_(1/2), W₂ZSiO_(1/2) and Z¹ ₃SiO_(1/2). The symbols W, Z and Z¹ are such as described hereinabove.

By way of examples of “M” terminal units, mention can be made of the trimethylsiloxy, dimethylphenylsiloxy, dimethylvinylsiloxy or dimethylhexenylsiloxy groups.

By way of examples of “D” units, mention can be made of the dimethylsiloxy, methylphenylsiloxy, methylvinylsiloxy, methylbutenylsiloxy, methylhexenylsiloxy, methyldecenylsiloxy or methyldecadienylsiloxy groups.

Said organopolysiloxanes A can be oils with a dynamic viscosity of about 10 to 100,000 mPa·s at 25° C., generally about 10 to 70,000 mPa·s at 25° C., or gums that have a molecular weight of about 1,000,000 mPa·s or more at 25° C.

All of the viscosities of which it is a question in this disclosure correspond to a magnitude of dynamic viscosity at 25° C. referred to as “Newtonian”, i.e. the dynamic viscosity that is measured, in a manner known per se, with a Brookfield viscometer with a shear speed gradient that is low enough so that the viscosity measured is independent of the speed gradient.

When entailing cyclical organopolysiloxanes, the latter are constituted of siloxyl “D” units of the following formulas: W₂SiO_(2/2), Z₂SiO_(2/2) or WZSiO_(2/2), which can be of the dialkylsiloxy, alkylarylsiloxy, alkylvinylsiloxy, alkylsiloxy type. Examples of such siloxyl units have already been mentioned hereinabove. Said cyclic organopolysiloxanes A have a viscosity of about 10 to 5000 mPa·s at 25° C.

According to a preferred embodiment, the composition X according to the invention comprises a second organopolysiloxane compound comprising, per molecule, at least two C₂-C₆ alkenyl radicals bonded to silicon atoms, different from the organopolysiloxane compound A, said second organopolysiloxane compound being preferably divinyltetramethylsiloxane (dvtms).

Preferably, the organopolysiloxane compound A has a mass content of Si-vinyl unit between 0.001 and 30%, preferably between 0.01 and 10%.

According to a preferred embodiment, the organohydrogenopolysiloxane compound B is an organopolysiloxane having at least two hydrogen atoms, per molecule, bonded to an identical or different silicon atom and, preferably, having at least three hydrogen atoms per molecule directly bonded to an identical or different silicon atom.

Advantageously, the organohydrogenopolysiloxane compound B is an organopolysiloxane comprising:

(i) at least two siloxyl units and, preferably, at least three siloxyl units of the following formula:

$\begin{matrix} {H_{d}Z_{e}^{3}{SiO}_{\frac{4 - {({d + e})}}{2}}} & \left( {B{.1}} \right) \end{matrix}$

in which:

-   -   d=1 or 2, e=0, 1 or 2 and d+e=1, 2 or 3,     -   the symbols Z³, which may be identical or different, represent a         monovalent hydrocarbon group having from 1 to 30 carbon atoms         and preferably chosen from the group consisting of alkyl groups         having from 1 to 8 carbon atoms and aryl groups containing         between 6 and 12 carbon atoms, and more preferably chosen from         the group consisting of a methyl, ethyl, propyl,         3,3,3-trifluoropropyl, xylyl, tolyl and phenyl radical, and

(ii) optionally at least one siloxyl unit of the following formula:

$\begin{matrix} {Z_{c}^{2}{SiO}_{\frac{4 - c}{2}}} & \left( {B{.2}} \right) \end{matrix}$

in which:

-   -   c=0, 1, 2 or 3,     -   the symbols Z², which may be identical or different, represent a         monovalent hydrocarbon group having from 1 to 30 carbon atoms         and preferably chosen from the group consisting of alkyl groups         having from 1 to 8 carbon atoms and aryl groups containing         between 6 and 12 carbon atoms, and more preferably chosen from         the group consisting of a methyl, ethyl, propyl,         3,3,3-trifluoropropyl, xylyl, tolyl and phenyl radical.

The organohydrogenopolysiloxane compound B can be formed solely of siloxyl units of formula (B.1) or in addition comprise units of formula (B.2). It can have a linear, branched, or cyclical structure. The degree of polymerisation is preferably greater than or equal to 2. More generally, it is less than 5000.

Examples of siloxyl units of formula (B.1) are in particular the following units: H(CH₃)₂SiO_(1/2), HCH₃SiO_(2/2) and H(C₆H₅)SiO_(2/2).

When it is a question of linear polymers, the latter are substantially constituted:

-   -   of siloxyl “D” units chosen from the units of the following         formulas Z² ₂SiO_(2/2) or Z³HSiO_(2/2), and     -   of siloxyl units “M” chosen from the units of the following         formulas Z² ₃SiO_(1/2) or Z³ ₂HSiO_(1/2).

These linear organopolysiloxanes can be oils with a dynamic viscosity of about 1 to 100,000 mPa·s at 25° C., generally about 10 to 5000 mPa·s at 25° C., or gums that have a molecular weight of about 1,000,000 mPa·s or more at 25° C.

When entailing cyclical organopolysiloxanes, the latter are constituted of siloxyl “D” units of the following formulas Z² ₂SiO_(2/2) and Z³HSiO_(2,2), which can be of the dialkylsiloxy or alkylarylsiloxy type or of Z³HSiO_(2/2) units only. They then have a viscosity of about 1 to 5000 mPa·s.

Examples of linear organohydrogenopolysiloxane compound B are: dimethylpolysiloxanes with hydrogenodimethylsilyl ends, dimethylhydrogenomethylpolysiloxanes with trimethylsilyl ends, dimethylhydrogenomethylpolysiloxanes with hydrogenodimethylsilyl ends, hydrogenomethylpolysiloxanes with trimethylsilyl ends, and cyclic hydrogenomethylpolysiloxanes.

For organohydrogenopolysiloxane compound B, particular preference is given to oligomers and polymers having the general formula (B.3):

in which:

-   -   x and y are an integer varying between 0 and 200,     -   the symbols R¹ which are identical or different, represent         independently of one another:         -   a linear or branched alkyl radical containing 1 to 8 carbon             atoms, optionally substituted by at least one halogen,             preferably fluorine, with the alkyl radicals being,             preferably, methyl, ethyl, propyl, octyl and             3,3,3-trifluoropropyl,         -   a cycloalkyl radical containing between 5 and 8 cyclical             carbon atoms,         -   an aryl radical containing between 6 and 12 carbon atoms, or         -   an aralkyl radical having an alkyl portion containing             between 5 and 14 carbon atoms and an aryl portion containing             between 6 and 12 carbon atoms.

Particularly suitable for the invention as an organohydrogenopolysiloxane compound B are the following compounds:

with a, b, c, d and e defined hereinbelow:

-   -   in the polymer of formula S1:         -   0≦a≦150, preferably 0≦a≦100, and more particularly 0≦a≦20,             and         -   1≦b≦90 preferably 10≦b≦80 and more particularly 30≦b≦70,     -   in the polymer of formula S2: 0≦c≦15     -   in the polymer of formula S3: 5≦d≦200, preferably 20≦d≦100, and         2≦e≦90, preferably 10≦e≦70.

In particular, the organohydrogenopolysiloxane compound B suitable for the invention is the compound of formula S1, where a=0.

Preferably the organohydrogenopolysiloxane compound B has a mass content of SiH unit between 0.2 and 91%, preferably between 0.2 and 50%.

In the framework of the invention, the proportions of organopolysiloxane A and of organohydrogenopolysiloxane B are such that the molar ratio of the hydrogen atoms bonded to the silicon (Si—H) in the organohydrogenopolysiloxane B to the alkenyl radicals bonded to the silicon (Si—CH═CH₂) in the organopolysiloxane A is between 0.2 and 20, preferably between 0.5 and 15, more preferably between 0.5 and 10 and even more preferably between 0.5 and 5.

In order to allow for the obtaining of material Y according to the invention, the composition X implements at least one catalyst C which is a complex corresponding to the following formula:

[Ni(L¹)₂]

in which:

-   -   the symbol Ni represents nickel at degree of oxidation II,     -   the symbols L¹, which may be identical or different, represent a         ligand which is a β-dicarbonylato anion or the enolate anion of         a β-dicarbonylated compound.

Note that at least one portion of the inventive nature of the invention, holds to the clever and advantageous selection of the structure of the catalyst C.

According to another preferred embodiment of the invention, the ligand L′ is an anion derived from a compound of formula (1): R¹COCHR²COR³ (1)

in which:

-   -   R¹ and R³, which may be identical or different, represent a         C₁-C₃₀ linear, cyclic or branched hydrocarbon radical, an aryl         containing between 6 and 12 carbon atoms, or a radical-OR⁴ with         R⁴ which represents a C₁-C₃₀ linear, cyclic or branched         hydrocarbon radical,     -   R² is a hydrogen atom or a hydrocarbon radical, preferably         alkyl, comprising from 1 to 4 carbon atoms; with     -   R¹ and R² can be connected in order to form a C₅-C₆ cycle, and     -   R² and R⁴ can be connected in order to form a C₅-C₆ cycle.

Advantageously, the compound of formula (I) is chosen from the group consisting of β-diketones: 2,4-pentanedione (acac); hexanedione-2,4; heptanedione-2,4; heptanedione-3,5; ethyl-3 pentanedione-2,4; methyl-5 hexanedione-2,4; octanedione-2,4; octanedione-3,5; dimethyl-5,5 hexanedione-2,4; methyl-6 heptanedione-2,4; dimethyl-2,2 nonanedione-3,5; dimethyl-2,6 heptanedione-3,5; 2-acetylcyclohexanone (Cy-acac); 2,2,6,6-tetramethyl-3,5-heptanedione (TMHD); 1,1,1,5,5,5-hexafluoro-2,4-pentanedione (F-acac)]; benzoylacetone; dibenzoyl-methane; 3-methyl-2,4-pentadione; 3-acetyl-pentane-2-one; 3-acetyl-2-hexanone; 3-acetyl-2-heptanone; 3-acetyl-5-methyl-2-hexanone; benzoylstearoylmethane; benzoylpalmitoylmethane; octanoylbenzoylmethane; 4-t-butyl-4′-methoxy-dibenzoylmethane; 4,4′-dimethoxy-dibenzoylmethane and 4,4′di-tert-butyl-dibenzoylmethane, and preferably from β-diketones 2,4-pentanedione (acac) and 2,2,6,6-tetramethyl-3,5-heptanedione (TMHD).

According to another preferred embodiment of the invention, the ligand β-dicarbonylato L¹ is a β-ketoesterato anion chosen from the group consisting of anions derived from the following compounds: methyl, ethyl, n-propyl, isopropyl, n-butyl, sec-butyl, isobutyl, tertiobutyl, isopentyl, n-hexyl, n-octyl, methyl-1 heptyl, n-nonyl, n-decyl and n-dodecyl esters of acetoacetic acid or those described in patent application FR-A-1435882.

According to a particularly preferred embodiment, the catalyst C is chosen from the complexes [Ni(acac)₂], [Ni(TMHD)₂], [Ni(ketoester)₂] and [Ni(Rhodiastab 50)₂]. It is understood that in the formulas hereinabove “acac” means the anion derived from the compound 2,4-pentanedione, “THMD” means the anion derived from the compound 2,2,6,6-tetramethyl-3,5-heptanedione, “ketoester” means the anion derived from a methyl ester of acetoacetic acid and “Rhodiastab 50” means a mixture of anions derived from the compound benzoylstearoylmethane, and of anions derived from the compound benzoylpalmitoylmethane.

The catalyst C can in particular be present in the composition X according to the invention in a content ranging from 0.001 to 10% molar of nickel per number of moles of C₂-C₆ alkenyl radicals bonded to silicon atoms of the organopolysiloxane compound A, preferably between 0.01 to 7%, and more preferably between 0.1 to 5%.

The composition X implemented in order to obtain the material Y according to the invention is preferably free of a catalyst based on platinum, palladium, ruthenium or rhodium. By the term “free” of a catalyst other than the catalyst C, it is understood that the composition X according to the invention comprises less than 0.1% by weight of catalyst other than the catalyst C, preferably less than 0.01% by weight, and more preferably less than 0.001% by weight, in relation to the total weight of the composition.

The composition X can advantageously include at least one adhesion promoter D.

Without limitation, it can be considered that the adhesion promoter D comprises:

-   -   (D.1) at least one alkoxy organosilane containing, per molecule,         at least one C₂-C₆ alkenyl group, or     -   (D.2) at least one organosilicon compound comprising at least         one epoxy radical, or     -   (D.3) at least one metal chelate M and/or a metal alkoxide of         general formula: M(OJ)n, with n=valency of M and J=C₁-C₈ linear         or branched alkyl,

M being chosen from the group formed by: Ti, Zr, Ge, Li, Mn, Fe, Al and Mg or mixtures thereof

In accordance with a preferred embodiment of the invention, the alkoxy organosilane (D.1) of the adhesion promoter D is selected from the products of the following general formula:

formula in which:

-   -   R1, R2, R3 are hydrogenated or hydrocarbon radicals which are         identical or different between them and represent a hydrogen         atom, a C₁-C₄ linear or branched alkyl or a phenyl optionally         substituted by at least one C₁-C₃ alkyl,     -   U is a C₁-C₄ linear or branched alkylene,     -   W is a valency bond,     -   R⁴ and R⁵ are radicals which are identical or different and         represent a C₁-C₄ linear or branched alkyl,     -   x′=0 or 1, and     -   x=0 to 2.

Without limitation, it can be considered that the vinyltrimethoxysilane is a particularly suitable compound (D.1).

Regarding the organosilicon compound (D.2), it is provided in accordance with the invention, to choose it:

a) either from the products (D.2a) having the following general formula:

formula in which:

-   -   R⁶ is a C₁-C₄ linear or branched alkyl radical,     -   R⁷ is a linear or branched alkyl radical,     -   y is equal to 0, 1, 2 or 3, and     -   X being defined by the following formula:

with:

-   -   E and D which are identical or different radicals chosen from         C₁-C₄ linear or branched alkyls,     -   z which is equal to 0 or 1,     -   R⁸, R⁹, R¹⁰ which are identical or different radicals that         represent a hydrogen atom or a C₁-C₄ linear or branched alkyl,         and     -   R⁸ and R⁹ or R¹⁰ that can alternatively form together and with         the two epoxy-carrying carbons, an alkyl cycle having from 5 to         7 membered ring, or

b) or from the products (D.2b) constituted of epoxyfunctional polydiorganosiloxanes comprising:

(i) at least one siloxyl unit of formula:

$\begin{matrix} {X_{p}G_{q}{SiO}\frac{4 - \left( {p + q} \right)}{2}} & \left( {D{.2}\mspace{14mu} {bi}} \right) \end{matrix}$

formula in which:

-   -   X is the radical such as defined hereinabove for the formula         (D.2 a)     -   G is a monovalent hydrocarbon group, free of unfavourable action         on the activity of the catalyst and chosen from alkyl groups         having from 1 to 8 carbon atoms inclusive, optionally         substituted by at least one halogen atom, and as well as among         the aryl groups containing between 6 and 12 carbon atoms,     -   p=1 or 2,     -   q=0, 1 or 2,     -   p+q=1, 2 or 3, and

and (ii) optionally at least one siloxyl unit of formula:

$\begin{matrix} {G_{t}{SiO}\; \frac{4 - r}{2}} & \left( {D{.2}\mspace{14mu} {bii}} \right) \end{matrix}$

formula in which G has the same meaning as hereinabove and r is equal to 0, 1, 2 or 3.

With regards to the last compound (D.3) of the adhesion promoter D, the preferred products are those of which the metal M of the chelate and/or of the alkoxide (D.3) is chosen from the following list: Ti, Zr, Ge, Li or Mn. It is to be underlined that titanium is more particularly preferred. It can be combined, for example, with an alkoxy radical of the butoxy type.

The adhesion promoter D can be formed from:

-   -   (D.1) alone     -   (D.2) alone     -   (D.1)+(D.2)

Or according to two preferred embodiments from:

-   -   (D.1)+(D.3)     -   (D.2)+(D.3)

and finally according to the most preferred embodiment: (D.1)+(D.2)+(D.3).

According to the invention, an advantageous combination for forming the adhesion promoter is the following:

-   -   vinyltrimethoxysilane (VTMO), 3-glycidoxypropyltrimethoxysilane         (GLYMO) and butyl titanate.

From a quantitative standpoint, it may be stated that the proportions by weight between (D.1), (D.2) and (D.3), expressed as a percentage by weight in relation to the total of the three, are the following:

-   -   (D.1)≧10, preferably between 15 and 70 and more preferably         between 25 and 65,     -   (D.2)≦90, preferably between 70 and 15 and more preferably         between 65 and 25, and     -   (D.3)≧1, preferably between 5 and 25 and more preferably between         8 and 18,

with the understanding that the sum of these proportions in (D.1), (D.2) and (D.3) is equal to 100%.

For better adhesive properties, the weight ratio (D.2):(D.1) is preferably between 2:1 and 0.5:1, with the ratio 1:1 being more particularly preferred.

Advantageously, the adhesion promoter D is present at a rate of 0.1 to 10% by weight, preferably 0.5 to 5% by weight, and more preferably between 1 to 3% by weight, in relation to the total weight of all of the constituents of the composition X.

According to a particular embodiment, the composition X implemented in order to obtain the material Y according to the invention also comprises at least one charge E.

The charges E optionally contained in the compositions according to the invention are preferably mineral. They can in particular be siliceous. Being siliceous materials, they can play the role of a reinforcing or semi-reinforcing charge. The siliceous reinforcing charges are chosen from colloidal silicas, silica powder for combustion and precipitation or mixtures thereof. These powders have an average particle size generally less than 0.1 μm (micrometres) and a BET specific surface area greater than 30 m2/g, preferably between 30 and 350 m2/g. The siliceous semi-reinforcing charges such as diatomaceous or crushed quartz earth, can also be used. With regards to non-siliceous mineral materials, they can intervene as a semi-reinforcing mineral charge or filler. Examples of these non-siliceous charges that can be used alone or in a mixture are carbon black, titanium dioxide, aluminium oxide, alumina hydrate, expanded vermiculite, unexpanded vermiculite, calcium carbonate optionally with a fatty acid surface treatment, zinc oxide, mica, talc, iron oxide, barium sulphate and slaked lime. These charges have a granulometry that is generally between 0.001 and 300 μm (micrometres) and a BET surface less than 100 m2/g. In a practical but not limiting way, the charges used can be a mixture of quartz and of silica. The charges can be treated with any suitable product. From a weight standpoint, it is preferred to implement a quantity of charge between 1% and 50% by weight, preferably between 1% and 40% by weight in relation to all of the constituents of the composition.

The invention as such also has for object, in the framework of this application, a crosslinkable composition X comprising:

-   -   at least one organopolysiloxane compound A comprising, per         molecule, at least two C₂-C₆ alkenyl radicals bonded to silicon         atoms,     -   at least one organohydrogenopolysiloxane compound B comprising,         per molecule, at least two hydrogen atoms bonded to an identical         or different silicon atom,     -   at least one catalyst C which is a complex corresponding to the         following formula:

[Ni(L¹)₂]

in which:

-   -   the symbol Ni represents nickel at degree of oxidation II,     -   the symbols L¹, which may be identical or different, represent a         ligand which is a β-dicarbonylato anion or the enolate anion of         a β-dicarbonylated compound,     -   optionally at least one adhesion promoter D and     -   optionally at least one charge E.

The composition X according to the invention can furthermore include one or several usual functional additives. As families of usual functional additives, mention can be made of:

-   -   silicone resins,     -   adherence modulators,     -   additives to increase consistency,     -   pigments, and     -   heat-resistant, oil-resistant or fire-resistant additives, for         example metal oxides.

Silicon resins are branched organopolysiloxane oligomers or polymers that are well known and available off the shelf. They have, in their structure, at least two different units chosen from those of formula R₃SiO_(1/2) (M unit), R₂SiO_(2/2) (D unit), RSiO_(3/2) (T unit) and SiO_(4/2) (Q unit), with at least one of these units being a T or Q unit.

The radicals R are identical or different and are chosen from C₁-C₆ linear or branched alkyl, hydroxyl, phenyl, trifluoro-3,3,3 propyl radicals. As alkyl radicals, mention can for example be made of methyl, ethyl, isopropyl, tertiobutyl and n-hexyl radicals.

As examples of branched organopolysiloxane oligomers or polymers, mention can be made of MQ resins, MDQ resins, TD resins and MDT resins, the hydroxyl functions can be carried by the M, D and/or T units. As an example of resins that are particularly well suited, mentioned can be made of hydroxyl MDQ resins that have their weight content in hydroxyl group between 0.2 and 10% by weight.

The materials Y according to the invention can in particular be obtained by introducing initially the catalyst C into the reaction medium, then by adding the organopolysiloxane A under stirring. Finally, the organohydrogenopolysiloxane compound B is introduced and the temperature of the mixture is increased in order to reach the crosslinking temperature. The mixture is maintained at the crosslinking temperature until the stopping of the stirring due to an increase in the viscosity of the mixture.

This invention also has for object a silicone composition crosslinking method, characterised in that it consists in heating the composition X such as defined hereinabove to a temperature of between 70 and 200° C., preferably between 80 and 150° C., and more preferably between 80 and 130° C.

The composition X implemented in order to obtain the material Y according to the invention has the advantage of not being sensitive to air and of being able as such to be implemented and in particular crosslink under a non-inert atmosphere, and in particular in air.

This invention is shown in detail in the non-limiting embodiments.

EXAMPLE 1: NICKEL BASED CATALYSTS FOR THE CROSSLINKING OF DIVINYLTETRAMETHYLSILOXANE (DVTMS) WITH MD′₅₀M

1) Constituents

1) Organopolysiloxane A: divinyltetramethylsiloxane (dvtms) (1.073 mole of vinyl radicals bonded to the silicon for 100 g of oil)

2) Organohydrogenopolysiloxane B of formula: MD′₅₀M (1.58 mole of hydrogen atoms bonded to the silicon for 100 g of oil), with: M: (CH₃)₃SiO_(1/2); and D′: (CH₃)HSiO_(2/2)

3) Catalysts (A), (B), (C), (D), (E) and (F):

The catalysts (A), (B), (C) and (D) are available off the shelf, for example under the references Strem purity >95% for the compound [Ni(acac)₂], Strem purity >98% for the compound [Ni(TMHD)₂].

The catalyst (E) is obtained via a synthesis that is well known to those skilled in the art:

The ketoester compound with R₁=Methyl and R₂=Methoxy (supplier: Sigma-Aldrich) is in a first step deprotonated using an equivalent of Bu-Li (supplier: Sigma-Aldrich) at low temperature (−78° C.). The salt obtained is re-crystallised in diethylether. The obtained deprotonated ligand (lithium salt) is added to a nickel chloride (NiCl₂) in solution in the THF at ambient temperature (12 h). After decantation, filtration and concentration, the complex is re-crystallised in the THF.

The complex [Ni(ketoester)₂] has the form of a green apple solid.

The catalyst (F) is also obtained by synthesis well known to those skilled in the art:

The diketone compound with R₁=Phenyl and R₂═C₁₇H₃₅ or C₁₅H₃₁ (supplier: Solvay) is in a first step deprotonated using an equivalent of Bu-Li (Supplier: Sigma-Aldrich) at low temperature (−78° C.). The salt obtained is re-crystallised in the diethylether. The obtained deprotonated ligand (lithium salt) is added to a nickel chloride (NiCl₂) in solution in the THF at ambient temperature (12 h). The complex obtained is viscous, with a green coloration. A step of re-crystallisation makes it possible to lead to the obtaining of a solid.

II) Formulations and Results:

For each formulation tested, the catalyst is weighed and introduced into a Schlenk at ambient temperature and under inert atmosphere when the complex is sensitive to air (case in particular with Ni(0)), or into a glass flask when the complexes are stable in air.

1.87 g of divinyltetramethylsiloxane (dvtms) then 1.27 g of oil MD′₅₀M are then introduced. The flask (or Schlenk) is placed under stirring in an oil bath that will be heated to the desired reaction temperature.

The ratio R corresponds to the molar ratio of the hydrogen atoms bonded to the silicon (Si—H) in the organohydrogenopolysiloxane (MD′₅₀M) to the alkenyl radicals (here vinyl) bonded to the silicon (Si—CH═CH₂) in the organopolysiloxane (dvtms).

The start of crosslinking is measured. The start of crosslinking is defined as being the stopping of the stirring due to an increase in the viscosity of the medium.

TABLE 1 Reaction % mol of Start of Catalyst temperature catalyst⁽¹⁾ Ratio R Atmosphere crosslinking Formulation 1 Ni(COD)₂] 110° C. 0.25% 1:1 Inert   3 h 20 (comparative) (under argon) Formulation 2 [Ni(TMHD)₂] 110° C. 0.25% 1:1 Non-inert 1 h (invention) Formulation 3 Ni(II) 110° C. 0.25% 1:1 Non-inert 45 h  (comparative) stearate Formulation 4 [Ni(acac)₂] 110° C. 0.25% 1:1 Non-inert 2 h (invention) ⁽¹⁾Expressed as a molar % of nickel per number of moles of vinyl radicals bonded to the silicon (Si—CH═CH₂) in dvtms

The comparative formulation 1 comprising a complex of Ni(0) crosslinks after 3h20 but must be maintained under inert atmosphere. Indeed, under a non-inert atmosphere, the complex breaks down very quickly, even before the start of the reaction, during the rise in temperature.

The formulations 2 and 4 according to the invention where the catalyst is a complex of Ni(II) having two β-dicarbonyl ligands crosslink in 1 to 2 h.

The comparative formulation 3, implementing a complex of Ni(II) having stearate ligands, crosslinks only after 45 h.

Furthermore the nickel catalysts according to the invention were tested in the following different operating conditions:

TABLE 2 Reaction % mol of Start of Catalyst temperature catalyst⁽¹⁾ Ratio R Atmosphere crosslinking Formulation 5 [Ni(TMHD)₂] 90° C.  0.25% 1:1 Non-inert Less than (invention) 15 h Formulation 6 [Ni(acac)₂] 90° C.  0.25% 1:1 Non-inert Less than (invention) 15 h Formulation 7 [Ni(TMHD)₂] 110° C.  0.125% 1:1 Non-inert Less than (invention) 15 h Formulation 8 [Ni(acac)₂] 110° C.  0.125% 1:1 Non-inert Less than (invention) 15 h Formulation 9 [Ni(ketoester)₂] 90° C.  0.25% 1:1 Non-inert 3.5 h (invention) Formulation 10 [Ni(ketoester)₂] 90° C. 0.125% 1:1 Non-inert Less than (invention) 15 h ⁽¹⁾Expressed as a molar % of nickel per number of moles of vinyl radicals bonded to the silicon (Si—CH═CH₂) in dvtms

The formulations 5 and 6 according to the invention show that a crosslinking is obtained at 90° C., even if this crosslinking is slower than that observed for formulations 2 and 4 carried out at 110° C.

The formulations 7, 8 and 10 according to the invention show that a crosslinking is obtained at 0.125% molar of catalyst, even if this crosslinking is slower than that observed for formulations 2, 4 and 9 comprising 0.25% molar of catalyst.

EXAMPLE 2: NICKEL BASED CATALYSTS FOR THE CROSSLINKING OF M^(VI) D₇₀ M^(VI) WITH MD′₅₀M I) Constituents

1) Organopolysiloxane A of formula M^(vi)D₇₀M (0.038 mole of vinyl radicals bonded to the silicon for 100 g of oil), with: Vi=Vinyl; M^(vi): (CH₃)₂ViSiO_(1/2) and D: (CH₃)₂SiO_(2/2)

2) Organohydrogenopolysiloxane B of formula: MD′₅₀M (1.58 mole of hydrogen atoms bonded to the silicon for 100 g of oil), with: M: (CH₃)₃SiO_(1/2); and D′: (CH₃)HSiO_(2/2)

3) Catalysts (A), (B), (C), (D), (E) and (F) such as defined in example 1.

II) Formulations and results:

For each formulation tested, the catalyst is weighed and introduced into a Schlenk at ambient temperature and under inert atmosphere when the complex is sensitive to air (case with Ni(0)), or into a glass flask when the complexes are stable in air.

Oil M^(vi)D₇₀M^(v1) then oil MD′₅₀M were then introduced.

For a ratio R corresponding to the molar ratio of the hydrogen atoms bonded to the silicon (Si—H) in the organohydrogenopolysiloxane (MD′₅₀M) to the alkenyl radicals (here vinyl) bonded to the silicon (Si—CH═CH₂) in the organopolysiloxane (M^(vi)D₇₀M^(vi)) of 1:1, 4.39 g of oil M^(vi)D₇₀M^(vi) then 0.105 g of oil MD′₅₀M were introduced.

The content in oil M^(vi)D₇₀M^(vi) and in oil MD′₅₀M were adjusted according to the ratio R desired.

The flask (or Schlenk) is placed under stirring in an oil bath that will be heated to the desired reaction temperature.

The ratio R corresponds to the molar ratio of the hydrogen atoms bonded to the silicon (Si—H) in the organohydrogenopolysiloxane (MD′₅₀M) to the alkenyl radicals (here vinyl) bonded to the silicon (Si—CH═CH2) in the organopolysiloxane (M^(vi)D₇₀M^(vi)).

The start of crosslinking is measured.

Study of the Duration of Crosslinking

TABLE 3 Reaction % mol of Start of Catalyst temperature catalyst⁽¹⁾ Ratio R Atmosphere crosslinking Formulation 11 [Ni(COD)₂] 110° C. 4% 1:1 Inert 2 h 50 (comparative) (under argon) Formulation 12 [Ni(TMHD)₂] 110° C. 4% 1:1 Non-inert 1 h 50 (invention) Formulation 13 Ni(II) 110° C. 4% 1:1 Non-inert No (comparative) stearate crosslinking at 48 h Formulation 14 [Ni(acac)₂] 110° C. 4% 1:1 Non-inert 2 h 20 (invention) ⁽¹⁾Expressed as a molar % of nickel per number of moles of vinyl radicals bonded to the silicon (Si—CH═CH₂) in the organopolysiloxane (M^(vi)D₇₀M^(vi))

The formulation 11 comprising a complex of Ni(0) crosslinks after 2h50 but must be maintained under inert atmosphere. Indeed, as already indicated in example 1, the complex breaks down very quickly under a non-inert atmosphere, even before the start of the reaction.

The formulations 12 and 14 according to the invention where the catalyst is a complex of Ni(II) having two β-dicarbonyl ligands crosslink after about 1h50 to 2h20.

The comparative formulation 13, implementing a complex of Ni(II) having stearate ligands, still does not crosslink after 48 h.

Furthermore the catalysts (E) and (F) according to the invention were tested in the following different operating conditions:

TABLE 4 Reaction % mol of Ratio Start of Catalyst temperature catalyst⁽¹⁾ R crosslinking Formulation [Ni(ketoester)₂] 110° C.   2%   1:1  5 h 15 (invention) Formulation [Ni(ketoester)₂] 110° C. 1.6% 1.6:1 30 min 16 (invention) Formulation [Ni(Rhodiastab)₂] 110° C. 0.8% 1.6:1  3 h 17 (invention) ⁽¹⁾Expressed as a molar % of nickel per number of moles of vinyl radicals bonded to the silicon (Si—CH═CH₂) in the organopolysiloxane (M^(vi)D₇₀M^(vi))

Study of the Effect of the Temperature

TABLE 5 Effect of the increase in temperature (1) Reaction % mol of Start of Catalyst temperature catalyst⁽¹⁾ Ratio R Atmosphere crosslinking Formulation 18 [Ni(TMHD)₂]  90° C. 2% 1:1 Non-inert 17 h (invention) Formulation 19 [Ni(TMHD)₂] 110° C. 2% 1:1 Non-inert 2 h 20 (invention) Formulation 20 [Ni(TMHD)₂] 130° C. 2% 1:1 Non-inert 10 min (invention) ⁽¹⁾Expressed as a molar % of nickel per number of moles of vinyl radicals bonded to the silicon (Si—CH═CH₂) in the organopolysiloxane (M^(vi)D₇₀M^(vi))

TABLE 6 Effect of the increase in temperature (2) Reaction % mol of Start of Catalyst temperature catalyst⁽¹⁾ Ratio R Atmosphere crosslinking Formulation 21 [Ni(acac)₂]  90° C. 1.6% 3.1:1 Non-inert 3 h (invention) Formulation 22 [Ni(acac)₂] 110° C. 1.6% 3.1:1 Non-inert 20 min (invention) Formulation 23 [Ni(acac)₂] 130° C. 1.6% 3.1:1 Non-inert 8 min (invention) ⁽¹⁾Expressed as a molar % of nickel per number of moles of vinyl radicals bonded to the silicon (Si—CH═CH₂) in the organopolysiloxane (M^(vi)D₇₀M^(vi))

The formulations 18 to 23 according to the invention show that the increase in temperature makes it possible to significantly reduce crosslinking time.

Study of the Effect of the Concentration in Catalyst

TABLE 7 effect of the increase in the concentration of catalyst (1) Reaction % mol of Start of Catalyst temperature catalyst⁽¹⁾ Ratio R Atmosphere crosslinking Formulation 24 [Ni(TMHD)₂] 110° C. 1% 1:1 Non-inert 26 h    (invention) Formulation 19 [Ni(acac)₂] 110° C. 2% 1:1 Non-inert 2 h 20 (invention) Formulation 12 [Ni(acac)₂] 110° C. 4% 1:1 Non-inert 1 h 50 (invention) ⁽¹⁾Expressed as a molar % of nickel per number of moles of vinyl radicals bonded to the silicon (Si—CH═CH₂) in the organopolysiloxane (M^(vi)D₇₀M^(vi))

TABLE 8 effect of the increase in the concentration of catalyst (2) Reaction % mol of Start of Catalyst temperature catalyst⁽¹⁾ Ratio R Atmosphere crosslinking Formulation 25 [Ni(TMHD)₂] 110° C. 0.16%  3.1:1 Non-inert 5 h (invention) Formulation 26 [Ni(acac)₂] 110° C. 0.4% 3.1:1 Non-inert 1 h 30 (invention) Formulation 27 [Ni(acac)₂] 110° C. 0.8% 3.1:1 Non-inert 1 h 20 (invention) Formulation 28 [Ni(acac)₂] 110° C. 1.6% 3.1:1 Non-inert 20 min (invention) Formulation 29 [Ni(acac)₂] 110° C. 3.1% 3.1:1 Non-inert 20 min (invention) ⁽¹⁾Expressed as a molar % of nickel per number of moles of vinyl radicals bonded to the silicon (Si—CH═CH₂) in the organopolysiloxane (M^(vi)D₇₀M^(vi))

The formulations 12, 19 and 24 to 29 according to the invention show that the increase in the concentration of catalyst makes it possible to significantly reduce crosslinking time. The formulation 25 further shows that the crosslinking can be observed even with very low catalyst contents, which makes it possible to prevent or limit the coloration of the crosslinked material.

Study of the Effect of the Ratio R

TABLE 9 Effect of the ratio R(1) Reaction % mol of Ratio Start of Catalyst temperature catalyst⁽¹⁾ R crosslinking Formulation 14 [Ni(acac)₂] 110° C. 4% 1:1 2 h 20 (invention) Formulation [Ni(acac)₂] 110° C. 4% 2:1 1 h 50 14a (invention) ⁽¹⁾Expressed as a molar % of nickel per number of moles of vinyl radicals bonded to the silicon (Si—CH═CH₂) in the organopolysiloxane (M^(vi)D₇₀M^(vi))

TABLE 10 Effect of the ratio R (2) Reaction % mol of Ratio Start of Catalyst temperature catalyst⁽¹⁾ R crosslinking Formulation 30 [Ni(acac)₂] 110° C. 1.6% 0.8:1  3 h (invention) Formulation 31 [Ni(acac)₂] 110° C. 1.6% 3.1:1 20 min (invention) ⁽¹⁾Expressed as a molar % of nickel per number of moles of vinyl radicals bonded to the silicon (Si—CH═CH₂) in the organopolysiloxane (M^(vi)D₇₀M^(vi))

The crosslinkings are carried out under a non-inert atmosphere. The formulations 14 and 14A, and 30 and 31 show that the increase in the ratio R makes it possible to reduce crosslinking time.

Duration of Crosslinking of Catalysts (A), (B), (E) and (F)

Finally, the crosslinking for the catalysts (A), (B), (E) and (F) was tested with a ratio R of 1.6:1. The results are presented in table 8.

TABLE 8 Reaction % mol of Ratio Start of Catalyst temperature catalyst⁽¹⁾ R crosslinking Formulation [Ni(acac)₂] 110° C. 1.6% 1.6:1 25-30 min 32 (invention) Formulation [Ni(TMHD)₂] 110° C. 1.6% 1.6:1 25-30 min 33 (invention) Formulation [Ni(cetoester)₂] 110° C. 1.6% 1.6:1 30 min 34 (invention) Formulation [Ni(Rhodiastab)₂] 110° C. 1.6% 1.6:1 2 h 30-3 h 35 (invention) ⁽¹⁾Expressed as a molar % of nickel per number of moles of vinyl radicals bonded to the silicon (Si—CH═CH₂) in the organopolysiloxane (M^(vi)D₇₀M^(vi))

The crosslinkings are carried out under a non-inert atmosphere. The formulations 32 to 35 show that the crosslinking is observed for different nickel based catalysts at the degree of oxidation (II).

EXAMPLE 3: CATALYST [NI(TMHD)₂] FOR THE CROSSLINKING OF M^(VI) D₃₅₀ M^(VI) WITH MD′₅₀M I) Constituents

1) Organopolysiloxane A of formula M^(vi)D₃₅₀M^(vi), with: Vi=Vinyl; M^(vi): (CH₃)₂ViSiO_(1/2) and D: (CH₃)₂SiO_(2/2)

2) Organohydrogenopolysiloxane B of formula: MD′₅₀M (1.58 mole of hydrogen atoms bonded to the silicon for 100 g of oil), with: M: (CH₃)₃SiO_(1/2); and D′: (CH₃)HSiO_(2/2)

3) Catalyst (A) such as defined in the example 1.

II) Formulations and Results:

We weighed 12.4 g of M^(vi)D₃₅₀M^(vi) with: Vi=Vinyl; M^(vi): (CH₃)₂ViSiO_(1/2) and D: (CH₃)₂SiO_(2/2) and 0.6 g of MD′₅₀M (1.58 mole of hydrogen atoms bonded to the silicon for 100 g of oil), with:

M: (CH₃)₃SiO_(1/2); and D′: (CH₃)HSiO_(2/2)

The ratio R corresponding to the molar ratio of the hydrogen atoms bonded to the silicon (Si—H) in the organohydrogenopolysiloxane (MD′₅₀M) on the alkenyl radicals (here vinyl) bonded to the silicon (Si—CH═CH₂) in the organopolysiloxane (M^(vi)D₃₅₀M^(vi)) of 10:1.

5 mol % of catalyst [Ni(TMHD)2] (expressed as a molar % of nickel per number of moles of vinyl radicals bonded to the silicon (Si—CH═CH₂) in the organopolysiloxane (M^(vi)D₃₅₀M^(vi))) is dissolved at ambient temperature in the oil MD′₅₀M and the mixture is incorporated at ambient temperature in the oil M^(vi)D₃₅₀M^(vi). The whole is placed in a Teflon mould then into an oven at 110° C.

After two hours, the crosslinked material is demoulded and its hardness (in Shore A) measured. The material has a hardness of 9 in Shore A degrees.

This example makes it possible to show that the implementing of catalysts claimed in crosslinking reactions of organopolysiloxane compound A with an organohydrogenopolysiloxane compound B allows for the obtaining of materials Y of which the hardness can be measured. 

1. Crosslinked silicone material Y obtained by heating to a temperature of between 70 and 200° C., preferably between 80 and 150° C., and more preferably between 80 and 130° C., a crosslinkable composition X comprising: at least one organopolysiloxane compound A comprising, per molecule, at least two C₂-C₆ alkenyl radicals bonded to silicon atoms, at least one organohydrogenopolysiloxane compound B comprising, per molecule, at least two hydrogen atoms bonded to an identical or different silicon atom, at least one catalyst C which is a complex corresponding to the following formula: [Ni(L¹)₂] in which: the symbol Ni represents nickel at degree of oxidation II, the symbols L¹, which may be identical or different, represent a ligand which is a β-dicarbonylato anion or the enolate anion of a β-dicarbonylated compound, optionally at least one adhesion promoter D and optionally at least one charge E.
 2. Crosslinked silicone material Y according to claim 1, wherein the catalyst C is present in a content ranging from 0.001 to 10% molar of nickel per number of moles of C₂-C₆ alkenyl radicals bonded to silicon atoms of the organopolysiloxane compound A, preferably between 0.01 to 7%, and more preferably between 0.1 to 5%.
 3. Crosslinked silicone material Y according to claim 1, wherein the composition X is free of catalyst based on platinum, palladium, ruthenium or rhodium.
 4. Crosslinked silicone material Y according to claim 1, wherein the ligand L¹ is an anion derived from a compound of formula (1): R¹COCHR²COR³  (1) in which: R¹ and R³, which may be identical or different, represent a C₁-C₃₀ linear, cyclic or branched hydrocarbon radical, an aryl containing between 6 and 12 carbon atoms, or a —OR⁴ radical with R⁴ which represents a C₁-C₃₀ linear, cyclic or branched hydrocarbon radical, R² is a hydrogen atom or a hydrocarbon radical, preferably alkyl, comprising from 1 to 4 carbon atoms; with R¹ and R² can be connected in order to form a C₅-C₆ cycle, and R² and R⁴ can be connected in order to form a C₅-C₆ cycle.
 5. Crosslinked silicone material Y according to claim 4, wherein the compound of formula (1) is chosen from the group comprising β-diketones: 2,4-pentanedione (acac); hexanedione-2,4; heptanedione-2,4; heptanedione-3,5; ethyl-3 pentanedione-2,4; methyl-5 hexanedione-2,4; octanedione-2,4; octanedione-3,5; dimethyl-5,5 hexanedione-2,4; methyl-6 heptanedione-2,4; dimethyl-2,2 nonanedione-3,5; dimethyl-2,6 heptanedione-3,5; 2-acetylcyclohexanone (Cy-acac); 2,2,6,6-tetramethyl-3,5-heptanedione (TMHD); 1,1,1,5,5,5-hexafluoro-2,4-pentanedione (F-acac)]; benzoylacetone; dibenzoyl-methane; 3-methyl-2,4-pentadione; 3-acetyl-pentane-2-one; 3-acetyl-2-hexanone; 3-acetyl-2-heptanone; 3-acetyl-5-methyl-2-hexanone; benzoylstearoylmethane; benzoylpalmitoylmethane; octanoylbenzoylmethane; 4-t-butyl-4′-methoxy-dibenzoylmethane; 4,4′-dimethoxy-dibenzoylmethane and 4,4′-di-tert-butyl-dibenzoylmethane, and preferably from ?-diketones 2,4-pentanedione (acac) and 2,2,6,6-tetramethyl-3,5-heptanedione (TMHD).
 6. Crosslinked silicone material Y according to claim 1, wherein the catalyst C is chosen from the complexes [Ni(acac)₂], [Ni(TMHD)₂], [Ni(ketoester)₂] and [Ni(Rhodiastab 50)₂], where “acac” means the anion derived from the compound 2,4-pentanedione, “THMD” means the anion derived from the compound 2,2,6,6-tetramethyl-3,5-heptanedione, “ketoester” means the anion derived from a methyl ester of acetoacetic acid and “Rhodiastab 50” means a mixture of anions derived from the compound benzoylstearoylmethane, and of anions derived from the compound benzoylpalmitoylmethane.
 7. Crosslinked silicone material Y according to claim 6, wherein the organopolysiloxane A comprises: (i) at least two siloxyl units (A.1), which may be identical or different, of the following formula: $\begin{matrix} {W_{a}Z_{b}{SiO}_{\frac{d - {({a + b})}}{2}}} & \left( {A{.1}} \right) \end{matrix}$ in which: a=1 or 2, b=0, 1 or 2 and a+b=1, 2 or 3; the symbols W, which may be identical or different, represent a C₂-C₆ linear or branched alkenyl group, and the symbols Z′, which may be identical or different, represent a monovalent hydrocarbon group having from 1 to 30 carbon atoms, and preferably chosen from the group consisting of alkyl groups having from 1 to 8 carbon atoms and aryl groups containing between 6 and 12 carbon atoms, and more preferably chosen from the group consisting of a methyl, ethyl, propyl, 3,3,3-trifluoropropyl, xylyl, tolyl and phenyl radical, (ii) and optionally at least one siloxyl unit of the following formula: $\begin{matrix} {Z_{a}^{1}{SiO}_{\frac{4 - a}{2}}} & \left( {A{.2}} \right) \end{matrix}$ in which: a=0, 1, 2 or 3, the symbols Z², which may be identical or different, represent a monovalent hydrocarbon group having from 1 to 30 carbon atoms and preferably chosen from the group consisting of alkyl groups having from 1 to 8 carbon atoms inclusive and aryl groups containing between 6 and 12 carbon atoms, and more preferably chosen from the group consisting of a methyl, ethyl, propyl, 3,3,3-trifluoropropyl, xylyl, tolyl and phenyl radical.
 8. Crosslinked silicone material Y according to claim 1, wherein the organohydrogenopolysiloxane compound B comprises at least three hydrogen atoms per molecule directly bonded to an identical or different silicon atom.
 9. Crosslinked silicone material Y according to claim 1, wherein the organohydrogenopolysiloxane compound B is an organopolysiloxane comprising: (i) at least two siloxyl units and, preferably, at least three siloxyl units of the following formula: $\begin{matrix} {H_{d}Z_{c}^{3}{SiO}_{\frac{4{({d + e})}}{2}}} & \left( {B{.1}} \right) \end{matrix}$ in which: d=1 or 2, e=0, 1 or 2 and d+e=1, 2 or 3, the symbols Z³, which may be identical or different, represent a monovalent hydrocarbon group having from 1 to 30 carbon atoms and preferably chosen from the group consisting of alkyl groups having from 1 to 8 carbon atoms and aryl groups containing between 6 and 12 carbon atoms, and more preferably chosen from the group consisting of a methyl, ethyl, propyl, 3,3,3-trifluoropropyl, xylyl, tolyl and phenyl radical, and (ii) optionally at least one siloxyl unit of the following formula: $\begin{matrix} {Z_{c}^{2}{SiO}_{\frac{4 - c}{2}}} & \left( {B{.2}} \right) \end{matrix}$ in which: c=0, 1, 2 or 3, the symbols Z², which may be identical or different, represent a monovalent hydrocarbon group having from 1 to 30 carbon atoms and preferably chosen from the group consisting of alkyl groups having from 1 to 8 carbon atoms and aryl groups containing between 6 and 12 carbon atoms, and more preferably chosen from the group consisting of a methyl, ethyl, propyl, 3,3,3-trifluoropropyl, xylyl, tolyl and phenyl radical.
 10. Crosslinked silicone material Y according to claim 1, wherein the composition X comprises a second organopolysiloxane compound comprising, per molecule, at least two C₂-C₆ alkenyl radicals bonded to silicon atoms, different from the organopolysiloxane compound A, said second organopolysiloxane compound being preferably divinyltetramethylsiloxane.
 11. Crosslinked silicone material Y according to claim 1, wherein the proportions of the organopolysiloxane A and of the organohydrogenopolysiloxane B are such that the molar ratio of the hydrogen atoms bonded to the silicon in the organohydrogenopolysiloxane B to the alkenyl radicals bonded to the silicon in the organopolysiloxane A is between 0.2 and 20, preferably between 0.5 and 15, more preferably between 0.5 and 10 and even more preferably between 0.5 and
 5. 12. Crosslinked silicone material Y according to claim 1, wherein, the composition X comprises one or several functional additives chosen from: silicone resins, adherence modulators, additives for increasing consistency, pigments, and heat-resistant, oil-resistant or fire-resistant additives, for example metal oxides.
 13. Use of the catalyst C such as described according to claim 1 as silicone composition crosslinking catalyst.
 14. Crosslinkable composition X comprising: at least one organopolysiloxane compound A comprising, per molecule, at least two C₂-C₆ alkenyl radicals bonded to silicon atoms, at least one organohydrogenopolysiloxane compound B comprising, per molecule, at least two hydrogen atoms bonded to an identical or different silicon atom, at least one catalyst C which is a complex corresponding to the following formula: [Ni(L¹)₂] in which: the symbol Ni represents nickel at degree of oxidation II; the symbols L¹, which may be identical or different, represent a ligand which is a β-dicarbonylato anion or the enolate anion of a β-dicarbonylated compound, optionally at least one adhesion promoter D and optionally at least one charge E.
 15. Method for crosslinking silicone compositions, comprising heating a composition X according to claim 14 to a temperature of between 70 and 200° C., preferably between 80 and 150° C., and more preferably between 80 and 130° C. 